An expansion joint is an apparatus that is situated between a device such as a boiler and a pipe and allows for expansion and contraction at the joint in order to account for movement of the pipe relative to the device. Expansion joints are used for example at power plants in order to couple boilers to steam pipes that are used to rotate generators. For example, power plants are configured to operate using steam having a temperature up to or exceeding approximately 1200 degrees Fahrenheit and pressure up to or exceeding 2000 PSI. Boiler systems may operate at this temperature, and at high pressure.
Seals are well known in the art for preventing leakage of fluid or contamination from one portion of an assembly to another. Seals can be provided by the use of adhesive sealants and mechanical devices such as gaskets, hermetic seals, labyrinth seals, wiper seals, or adhesive sealants. Depending on the type of seal used and the application, movement of components, high pressures, high temperatures and other environmental conditions may cause significant wear. In some applications, seals may be exposed to sufficiently high pressure or temperature, making use of traditional seals unsuitable. In some applications, a seal may be desired for use around a moving member, and these traditional seals may be too rigid to adequately seal the area while allowing movement of the components.
In the past, pipes, cylinders or rods which penetrate a pressure boundary may require a certain amount of movement relative to the pressure boundary. In these environmental conditions a seal may be used which is formed of a fabric sleeve which is vulnerable to failure in high temperature environments. Alternatively, a metal bellows seal may be utilized which has a limited fatigue life before cracking. Alternatively, a mechanical seal may be utilized which has undesirable tolerances between the seal and the pipe, cylinder, or rod, resulting in substantial leakage. Mechanical seals are subject to tolerance controlled leakage. Mechanical seals may utilize a packing-gasket like material which may experience wear and increase the dimensions for a gap between a pipe and sealing member. In the past, seals which attempt to simultaneously control leakage flow, corrosion, temperature, and gas leakage have experienced marginal reliability.